Well, here's the idea: You allow the Civil War questline to end instantly by killing one of the leaders.
The average joe with Imperial leanings can proceed in two ways.
1. Assuming the Imperial supporter is in the Dark Brotherhood, after killing the Emperor, you can drop a axe by his body, thus giving the blame to the Stormcloaks. In retaliation, the Legion troopers present will directly attack Windhelm and win.
2. If he doesn't feel like it, he might as well make the ritual to get the Emperor assassinated. But, in order to success, you'll need a axe to give to the assassin.
While the Stormcloak ultranationalist might have it easier, it's the only way, unfortunately. What he needs to do? Infiltrate the Palace of the Kings, kill Ulfric in his sleep, drop a Imperial sword and watch as the rebels automatically win the Civil War.
Simple as that.